What I've Learned Buying Silicone: Window Strips, Rubber Mounts, and When RTV Is Worth the Premium

Why there isn't a single right answer

I'll give you the framework I actually use. It's not elegant—one question, three branches, and some guesswork at the edges. For context: I'm the office administrator for a 260-person manufacturing company. I manage close to $180K in annual purchases across 8 vendors, and I report to both operations and finance. My choices need to hold up in a budget review, not just on a spec sheet.

When someone asks me to "buy some silicone," three scenarios show up in my inbox. Yours probably fits one of them.

Scenario 1: Regular, low-cost purchases (window rubber strip, rubber mounts)

This is the high-volume, low-dollar stuff. Door seals, window rubber strip, rubber mounts for equipment, general maintenance items. Ordered maybe 60-80 times a year, usually under $200 per order. Most buyers treat these as commodity purchases. I used to as well. Then I learned the specs matter more than the label on the box.

What actually matters in this scenario:

• Material classification. ASTM D2000 is the rubber classification standard. If your supplier can't tell you which callout they're meeting, that's not a supplier—that's a reseller. The callout describes hardness (Shore A), tensile strength, and heat resistance in one line.
• Temperature range. Standard EPDM handles roughly -50°C to +150°C. Silicone rubber grades stretch to -55°C to +200°C. If you only brief a supplier on "rubber strip," you'll get EPDM when you wanted silicone—or the reverse at three times the cost.
• Shore A hardness. For rubber mounts, this is the spec that ruins your afternoon if you don't check it. A 40 Shore A mount and a 70 Shore A mount are not interchangeable. Different vibration profiles, different failure modes.

The mistake I made here, in 2022: I saved $60 on a window rubber strip order by going with a cheaper vendor. "Same spec," they said. Three months later, the strip had cracked along the compression zone. I replaced strips on 18 windows at $400 plus labor—inside a quarter where I was already over budget.

Their spec sheet listed "EPDM, 60 Shore A." Fine on paper. But the actual compound behaved closer to 75 Shore A at low temperatures. The lesson wasn't "don't buy cheap." It was: verify batch consistency, not just the spec sheet on the quote.

Scenario 2: Critical sealing applications—when Momentive RTV silicone earns the premium

RTV stands for room-temperature vulcanizing. It cures at ambient temperature, either by absorbing moisture (one-part) or through mixing (two-part). This is the category where brand names start to matter.

I buy Momentive RTV silicone for specific industrial sealing applications—electrical enclosure gaskets, HVAC duct seals, and any joint where failure means downtime. Brand-name RTV silicone typically runs 20-40% above generic equivalents on comparable orders. It is not the cheapest option.

When I pay for it:

• Temperature cycling is tight. Generic RTV often works fine to 150°C. Certain Momentive RTV formulations hold past 200°C, and their data sheets document cycle counts, not just peak temperature.
• Failure is invisible. Enclosure gaskets on equipment that ships out, for instance. If that seal fails, it's a warranty event, not a maintenance ticket.
• You can document the material source. This matters more than I expected. Our quality team now asks for material certificates. If the RTV has a traceable lot and a manufacturer login portal, that's one less audit hole.

When I don't pay for it: Most of our RTV purchases don't need the brand-name tier. For non-critical seals—interior door frames, non-hazardous enclosures—a generic silicone RTV from a reputable supplier performs fine. I used to think "Momentive means quality, so buy Momentive everywhere." That's wasted budget.

About the momentive login portal: This is the one part of the buying process I actually like. Order tracking, material certificates, and invoice history in one place. For a procurement role like mine, that's the difference between spending Tuesday morning chasing documents and spending it on something that moves the needle. You'll need your account number from your distributor—they set it up—then it's a straightforward dashboard.

Small warning: the momentive login portal is useful for order history and certificates. It doesn't replace a distributor. You'll still place the order through them; the portal confirms and tracks.

Even after we placed our first Momentive order, I second-guessed the decision for a week. What if a generic RTV held just as well? It wasn't until the scheduled maintenance cycle eighteen months later—no visible degradation, seal intact—that I finally stopped worrying about it.

Scenario 3: Is TPU silicone? (And which one do you actually need)

Short answer: no. TPU is thermoplastic polyurethane. Silicone is a silicone elastomer. They are chemically unrelated and behave differently in almost every dimension that matters. I've fielded this question three times this year from colleagues who read a materials article and came away confused.

The comparison that actually helps:

• TPU beats silicone on abrasion and tear resistance. Conveyor parts, drill guides, cable jacketing—mechanical contact applications favor TPU.
• Silicone beats TPU on temperature stability. Standard silicone handles -55°C to +200°C. Standard TPU softens near 80°C and takes a permanent set above 100°C.
• Silicone is chemically inert. Food-contact surfaces, medical-adjacent equipment, aggressive fluid exposure—silicone wins.
• TPU is easier to recycle and usually cheaper per unit. High-volume, mechanically simple applications often justify it.

My rule for this decision: Temperature cycling, chemical exposure, or long field life = silicone. Mechanical wear, abrasion, cost sensitivity = TPU. When in doubt, compare Shore A or D hardness, tensile strength, and actual service temperature on the datasheet—don't trust the marketing name.

How to figure out which scenario you're in

Here's the checklist I use. Apply it in order:

1. Replacement part or new design? Replacement means Scenario 1 unless the original failed for temperature or chemical reasons. New design means Scenario 2 or 3.
2. What's the failure cost? If a bad seal costs under $500 and doesn't reach a customer, buy on spec, not brand. If it can trigger a warranty claim or a shutdown, pay the premium.
3. Does the material need temperature extremes or chemical resistance? That's the silicone column. If not, look at TPU or EPDM first—usually cheaper and often adequate.
4. Can your quality team audit the source? For brand-name supplier purchases, the momentive login portal makes this easy. If you're buying through a reseller with no lot traceability, decide whether the risk is acceptable for this specific application.

I've been wrong on this before. In 2023, I bought generic RTV for a gasketing job I assumed was low-stakes—interior ductwork. Temperature stability wasn't documented on the data sheet, and the seal cracked in six months. $1,200 of rework for a $90 order. That kind of mistake teaches you to appreciate a supplier who can hand you a datasheet with a certificate attached.

One last thing

The materials themselves haven't changed much—silicone still behaves like silicone, and EPDM still behaves like EPDM. But the buying process has. Five years ago I was making phone calls and hoping someone would fax a spec sheet. Now much of that data lives in a portal. The fundamentals of matching specification to application are unchanged; the execution has gotten faster.

The people who still lose money on this aren't the ones who don't know brand names. They're the ones who don't verify the spec. Start with the application, work backward to the material, then pick the supplier. That order doesn't change, no matter what the portal looks like.